Hi,
 
I am kind of new here. I looked at the archive and found
"simple and powerful IR transmitter" from Enrique Vidal
(01/26/2001 11:04:23).
 
Are there still interests in this subject? I have two suggestions.
 
(1) Like DTR, the signals RTS and TX can also be connected
to the negative side of the 4000uF capacitor through diodes.
TX is normally negative, but we have to make sure that the
software drives RTS negative too.
 
Ever little bit helps!
 
(2) We can eliminate (short) the 22 Ohm resistor and one of
the two IR emitting diodes. In stead, we add an inductor
between the collector of the PNP transistor and the remaining
IR emitting diode. Also add a Schottkey diode from negative
side of the 4000uF capacitor to the collector of PNP. The
software needs to reduce the duty cycle from 50% to about
25%.
 
This is how it works. When the PNP turns on, there is no
resistor to limit the current, but the inductor will. The
energy that was wasted in the resistor is now stored in
the inductor (in the form of magnetic field). When the PNP
turns off, the inductor will force the Shottkey diode and
the IR emitting diode going for a short while without
discharging the capacitor anymore. This is free energy!
 
-- Lichen